Electrostatic grounding devices for tables, equipment, and the like



y 3, 1956 w. G. LEGGE ELECTROSTATIC GROUNDING DEVICES FOR TABLES.EQUIPMENT. AND THE LIKE Filed Jan 15 1953 IN V EN T OR. P16452221? LEGGZBY jrrafin lm MPW ELECTROSTATIC GROUN DING DEVICES FOR TABLES,EQUIPMENT, AND THE LIKE Walter G. Legge, Brooklyn, N. Y.

Application January 15, 1953, Serial No. 331,457

1 Claim. (Cl. 317--2) This invention relates to grounding devices forconducting electrostatic charges from tables, chairs, benches,mechanical and electrical equipment and the like to the conductivesupporting surface or flooring.

An object of the invention is to provide an effective grounding devicewhich will permit of the flow of electrostatic charges from articles ofsaid character to the the supporting surface or flooring and which willprevent the upward flow of a high potential current.

Operating tables, anesthetic equipment in hospitals, and tables, chairs,benches and the like in laboratories and ordnance factories may becomecharged with static electricity if the legs supporting the same areinsulated from the conductive supporting surface by nonconductivecasters or non-conductive floor surfacing. Furthermore, such articlesare frequently moved about and if not properly grounded may endanger theoccupants, or physicians or workmen by the articles coming in contactwith a source of high potential current or by the accumulation of staticelectricity of suflicient intensity to produce a spark so as to ignitecombustible gases in the room or inflammable liquids being used in theroom. An object of the present invention, therefore, is to provideprotection for those in a room where such articles are used or who mayoccupy the same, by insuring that the articles are satisfactorilygrounded at all times when disposed in a stationary position or whenbeing moved from place to place.

Another object of the invention is to provide a device of said characterwhich is adjustable for attachment to articles of different heights andwhich is weighted for frictional engagement with the supporting orconductive surface to thereby insure proper electrical contact therewithat all times.

With the foregoing and other objects in view, reference is now made tothe following specification and accompartying drawings in which thepreferred embodiments of the invention are illustrated.

In the drawings:

Fig. l is a perspective view of a table provided with an electrostaticgrounding device constructed in accordance with the invention.

Fig. 2 is an enlarged view partially in section and parts broken away ofthe electrostatic grounding device.

Fig. 3 is a sectional view taken approximately on line 3-3 of Fig. 2.

Fig. 4 is a view similar to Fig. 2 of another modified form ofelectrostatic rounding device.

Fig. 5 is a sectional view taken approximately on line 5--5 of Fig. 4.

The floorings in hospitals, laboratories, ordnance plants and the likeare usually of conductive material so as to form a good ground, or suchfloorings have conductive bars embedded therein and exposed at thesurface, the bars being connected with a water pipe and the like forgrounding the flooring. Referring to the drawings by characters ofreference, the grounding device indicated generally by the referencecharacter is shown in its United States atent O ice;

application to the grounding of a table such as a hospital operatingtable T which is supported on a conductive flooring F. The groundingdevice 10 is made of non-sparking metal such as brass, copper, or othermetal which will not emit sparks in the event that a piece of flint orthe like should accidentally strike the same.

The grounding device includes a hook 11 adapted to engage the metalframe of the table and which is connected with a metallic groundingmember 13 by a flexible conductor 14. The flexible conductor consists ofa conductor wire or chain as illustrated and a tensioning member 15 anda resistor 16 which are interposed between sections of the flexibleconductor. The combined length of the flexible conductor 14 and thegrounding member 13 is greater than the distance from the engagement ofthe hook 11 with the metal frame of the table to the supporting surfaceor flooring, whereby the grounding member will be canted when inengagement with the supporting surface. The grounding member 13 may beof solid formation or the same may be of tubular formation and have afilling of lead or other metal to weight the same. The said groundingmember is constructed to provide a socket at its lower end in which ametallic ball or sphere 17 is rollably fitted. The ball 17 beingweighted by the grounding member provides a positive contact with thesupporting surface for grounding the table T and when the table is movedthe ball 17 will have rolling contact with the supporting surface forfree rolling movement thereover and for providing a positive groundingof the table.

The tensioning member 15 includes inner and outer telescopicallyassociated cylindrical tubes 18 and 19 which are linked with theconductor sections 20 and 21 respectively and have a coil spring 22arranged within the innermost tube and secured at its ends to the endwalls of the tubes respectively. The spring is in tensioned retractedrelation so as to permit of sliding movement of the tubes with referenceto each other. The resistor 16 is located adjacent the grounding member13 and is interposed between the conductor sections 21 and 25. Theresistor permits the passage of electrostatic charges but prevents theupward flow of a high electric current from the grounding member 13.

The coil spring 22 is suflicient to maintain the flexible conductor 14in taut condition so as to prevent sagging thereof and a positiveelectrical connection of all the parts forming the flexible conductor.The resistor 16 includes a resistance wire 27 which is connected at itsends with the conductor sections 21 and 25 and which constitutes asafety fuse having a resistance which will prevent an excessive currentflowing therethrough in the event that the grounding member 13 came intocontact with a high potential conductor. The resistance 27 may be of250,000 ohms and may vary from 50,000 to 2,000,000 ohms depending uponthe use to be made of the grounding device. The flexible conductor 14includes a split ring 28 adjacent the hook 11 and one of the linksintermediate the hook 111 and the tensioning member 15 is provided witha relatively small hook 29 which is adapted to engage the split ring 28for shortening the flexible conductor when the article to which it is tobe attached is of reduced height.

The grounding device may be as indicated in Figs. 4 and 5 of thedrawings, which similarly includes a clamp 30, a grounding member 31,and a flexible conductor 32 interposed between the clamp and thegrounding member and connected therewith. The flexible conductor mayalso include a tensioning member 33 and a resistor 34 similar to thetensioning member 15 and resistor 16 in the previous form of theinvention. In this form of the invention, however, the grounding member31 includes a metallic bar 35 and a base 36, the base being approxi- Jmately 6" in diameter or in cross-sectional dimension for engagementwith conductive members embedded in composition flooring. The metallicbar may be of solid formation or the same may be of tubular formationand have a filling of lead or other metal to weight the same. The base36 is made of sheet metal to provide a peripheral flange 37 and anupstanding hollow central portion 38. The metallic bar 35 is connectedwith the base 36 centrally thereof for free or universal swingingmovement of the bar with reference to the base. For this purpose, thebar is provided with a chain 40 which extends downwardly through anopening 41 in the base and is engaged by a pin 42 within the upperportion 38 of the base for retaining the bar and base in assembledrelation.

What is claimed is:

In a grounding device for an article of the character described, aflexible conductor affixed at its upper end to said article, aconductive grounding member including a surface engaging member and aweighted metallic body, said surface engaging member having a broad flatbottom face adapted to slideably engage the surface on which the articleis supported and said metallic body being connected with the lower endof said flexible conductor, means connecting said surface engagingmember and said metallic body for relative movement therebetween and forimposing the weight of said metallic body on said surface engagingmember, and said flexible conductor including an insulated resistancefor preventing high electrical charges passing beyond said resistanceand upwardly of the flexible conductor.

References Cited in the file of this patent UNITED STATES PATENTS993,447 Hotchkiss May 30, 1911, 2,084,523 Crawford June 22, 19372,325,414 McChesney July 27, 1943 2,502,496 Wickman Apr. 4, 19502,586,747 Van Atta Feb. 19, 1952 FOREIGN PATENTS 746,925 France June 8,1933

